Obtaining PMA for TSO Articles

If you're a manufacturer looking at producing a replacement part for a TSO-approved article — or a component that goes inside one — the approval path is a Parts Manufacturer Approval. But the relationship between a TSO and a PMA isn't obvious, and getting it wrong can send a program down the wrong path before it starts.

This post explains how TSO articles fit into the certification structure, where the PMA opportunity actually sits, and why the complexity of the article determines whether you're reproducing the whole thing or a part within it.

How TSO Articles Get Installed in the First Place

A Technical Standard Order is an FAA minimum performance standard for a specific type of article — an appliance, a component, a piece of equipment. A manufacturer obtains a TSO Authorization (TSOA) to produce that article in conformance with that standard.

But the TSO is only one piece of the picture. The TSO article gets installed in a product — an aircraft, an engine — under that product's Type Certificate. The TC holder includes the TSO article as part of their type design. The installation is approved through the TC, not through the TSO. The TSO says "this article meets this performance standard." The TC says "this article is approved as part of this product's type design."

So the OEM produces the TSO article, the TC holder incorporates it into the product, and the installation is approved. No PMA is involved — the article and its installation are covered by the TSOA and the TC respectively.

Where PMA Enters the Picture

PMA enters the picture when a third party — someone who is not the OEM or the TC holder — wants to produce a replacement. The third party reverse-engineers the article, or a part within it, and obtains a PMA to manufacture and sell it as an approved replacement.

The PMA traces to the product in which the article is installed. Whether you're reproducing a complete TSO article or a single component inside one, the PMA ties back to the product's type certificate — Part 23 for a normal-category airplane, Part 25 for a transport-category airplane, Part 27 or Part 29 for rotorcraft, or Part 33 if the article installs into an engine.

This is the key: the PMA isn't tied to the TSO. It's tied to the product the TSO article is installed in.

What Determines the PMA Opportunity: Article Complexity

Not every PMA for a TSO-related part looks the same, and the complexity of the TSO article is what determines where the real opportunity sits.

Simpler TSO articles — a filter, a valve, a less complex component — can realistically be reverse-engineered and reproduced in their entirety. A third-party manufacturer can produce the whole article as a PMA replacement. The PMA substantiation demonstrates that the reproduced article meets the applicable airworthiness standards for the product it installs into, following the identicality or test and computations path like any other PMA.

Complex TSO articles — like an APU, or a sophisticated avionics unit — are a different story. No third party is going to reverse-engineer and reproduce an entire auxiliary power unit. The engineering scope, the cost, and the certification burden make reproducing the full article impractical.

But the parts inside that complex article are another matter entirely. An APU is made up of hundreds of individual components — gaskets, O-rings, seals, bearings, fuel nozzles, hardware, fittings. Each of those is a potential PMA candidate. A third party can reverse-engineer a gasket that goes inside an APU and obtain a PMA for that gasket as a replacement part. The PMA traces through the chain: the PMA part installs into the TSO article (the APU), which installs into the aircraft (under the TC).

This is where much of the practical PMA opportunity around complex TSO articles actually lives — not at the article level, but at the component level within it.

Why This Matters Commercially

The commercial implication is worth stating plainly: every complex TSO article installed in an aircraft fleet is a collection of individually replaceable parts, and each of those parts is a potential PMA opportunity.

Take the APU example. An operator doesn't replace the entire APU because a seal wears out — they replace the seal. And if the OEM seal is expensive, back-ordered, or hard to source, the operator looks for an approved alternative. That approved alternative is a PMA part.

Multiply that across the components inside a single APU, then across the fleet of aircraft that use that APU, and the addressable market becomes clear. The same logic applies to any complex TSO article — the article itself may be untouchable as a PMA target, but the parts inside it aren't.

For manufacturers evaluating where to enter the aftermarket, this is a useful lens: don't look at the TSO article as a single monolithic target. Look at what's inside it, what wears, what gets replaced, and what the OEM supply situation looks like for those individual components. That's where the viable PMA candidates are.

How the PMA Process Works

The PMA process for a TSO-related part follows the same two compliance paths as any other PMA — identicality or test and computations. What changes is the traceability chain.

For a simple TSO article reproduced in its entirety, the PMA substantiation demonstrates that the replacement article meets the applicable airworthiness standards for the product it installs into. Straightforward.

For a component inside a complex TSO article, the substantiation still has to close against the applicable airworthiness standards — but the traceability runs through the TSO article to the product. The PMA part goes into the APU, the APU goes into the aircraft, and the airworthiness standards the PMA has to satisfy are those of the aircraft's type certificate. A DER helps scope exactly which requirements apply given where the part sits in that chain, and what level of substantiation the FAA expects.

Where Prime Propulsion Fits

Our in-house DER has propulsion certification experience from inside the FAA and in private industry, with delegation across Parts 23, 25, 27, 29, and 33. We help manufacturers who are evaluating PMA opportunities around TSO articles — whether that's reproducing a simpler article in its entirety or targeting specific components inside a complex one like an APU.

The scoping question — which part, which traceability chain, which airworthiness standards, which compliance path — is the first and most important decision in any of these projects. Getting it right early is the difference between an efficient program and one that generates FAA comments and costs months.

If you have a TSO-related part you're considering as a PMA candidate and want to understand what the path looks like, contact us — there's no cost to scope it out. You can also read the Ultimate Guide to FAA PMA Certification for a step-by-step look at the full PMA process.

Prime Propulsion delivers expert FAA certification solutions for small to medium-sized aerospace firms. Our DER-led team specializes in PMA, STC, Test Cell Correlations, and Repair Specification support.